[PATCH perf-tools-next 0/3] perf trace: Symbolise kernel virtual addresses and function pointers

[PATCH perf-tools-next 0/3] perf trace: Symbolise kernel virtual addresses and function pointers

[Aaron Tomlin]

Hi Namhyung, Arnaldo, Ian,

This has been rebased against perf-tools-next/perf-tools-next.
Kindly ignore the previous submission [1].

[1]: https://lore.kernel.org/lkml/20260803210842.245789-1-atomlin@atomlin.com/#r

When inspecting kernel execution flows using perf trace (e.g., when
monitoring workqueues delayed work items, timer callbacks, etc.),
tracepoint payload arguments containing raw kernel virtual addresses are
currently rendered as hexadecimal values (e.g., 0xffffffff81234567).

This requires manual symbol lookups against /proc/kallsyms or vmlinux to
identify the underlying kernel function being executed.

This patch series enhances perf trace by introducing kernel virtual
address and function pointer symbolisation using perfs native symbol
engine (i.e., machine__find_kernel_symbol()).

    Before:
      workqueue:workqueue_execute_end(work: 0xffffffffab2f1420, function: 0xffffffffa8046b50)

    After:
      workqueue:workqueue_execute_end(work: 0xffff8ac2c420f270, function: wb_update_bandwidth_workfn)

Patch 1 adds the syscall_arg__scnprintf_ksym (SCA_KSYM) beautifier
which resolves virtual addresses via machine__find_kernel_symbol(),
formatting them as symbol_name+offset (or "NULL" with a hex fallback).

Patch 2 updates event format initialisation in
syscall_arg_fmt__init_array() to automatically assign SCA_KSYM to
tracepoint fields named function, fn, work, action, or callsite,
as well as fields typed as function pointers.

Patch 3 extends BTF pretty-printing in trace__btf_scnprintf() with
btf_is_func_ptr() to automatically detect BTF function prototypes and
symbolise kernel function pointers without requiring manual field table
configuration.

Aaron Tomlin (3):
  perf trace: Introduce kernel symbol beautifier for virtual addresses
  perf trace: Auto-assign kernel symbol beautifier to function pointer
    fields
  perf trace: Enhance BTF type formatting to symbolise kernel function
    pointers

 tools/perf/builtin-trace.c       | 76 ++++++++++++++++++++++++++++----
 tools/perf/trace/beauty/beauty.h |  3 ++
 2 files changed, 71 insertions(+), 8 deletions(-)

-- 
2.55.0

[PATCH perf-tools-next 1/3] perf trace: Introduce kernel symbol beautifier for virtual addresses

[Aaron Tomlin]

Currently, when perf trace formats tracepoint payloads or system call
arguments containing raw kernel virtual addresses (e.g., a work item
function pointer work_func_t in workqueue:workqueue_execute_start),
it prints them as raw hexadecimal values (e.g., 0xffffffff81234567).
This impairs readability when tracing kernel execution flows.

Introduce a dedicated kernel symbol beautifier,
syscall_arg__scnprintf_ksym (i.e., SCA_KSYM), to resolve kernel
virtual addresses to human-readable symbol names and offsets
(e.g., flush_to_ldisc).

The beautifier looks up the virtual address in the machine kernel maps via
machine__find_kernel_symbol(). If a valid kernel symbol is found, the
symbol name and offset are printed without requiring --libtraceevent; if
the address is zero, "NULL" is rendered; otherwise, it gracefully falls
back to hexadecimal formatting.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 tools/perf/builtin-trace.c       | 24 ++++++++++++++++++++++++
 tools/perf/trace/beauty/beauty.h |  3 +++
 2 files changed, 27 insertions(+)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index c3c7f1f85c53..102221b301a5 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -750,6 +750,30 @@ size_t syscall_arg__scnprintf_ptr(char *bf, size_t size, struct syscall_arg *arg
 	return syscall_arg__scnprintf_hex(bf, size, arg);
 }
 
+size_t syscall_arg__scnprintf_ksym(char *bf, size_t size, struct syscall_arg *arg)
+{
+	if (arg->val == 0)
+		return scnprintf(bf, size, "NULL");
+
+	if (arg->trace && arg->trace->host) {
+		struct map *map;
+		struct symbol *sym = machine__find_kernel_symbol(arg->trace->host,
+								 arg->val, &map);
+
+		if (sym) {
+			u64 start = map__unmap_ip(map, sym->start);
+			u64 offset = arg->val - start;
+
+			if (offset == 0)
+				return scnprintf(bf, size, "%s", sym->name);
+			return scnprintf(bf, size, "%s+0x%" PRIx64,
+					 sym->name, offset);
+		}
+	}
+
+	return syscall_arg__scnprintf_hex(bf, size, arg);
+}
+
 size_t syscall_arg__scnprintf_int(char *bf, size_t size, struct syscall_arg *arg)
 {
 	return scnprintf(bf, size, "%d", arg->val);
diff --git a/tools/perf/trace/beauty/beauty.h b/tools/perf/trace/beauty/beauty.h
index 58a3206481ae..0f4801c61a5b 100644
--- a/tools/perf/trace/beauty/beauty.h
+++ b/tools/perf/trace/beauty/beauty.h
@@ -160,6 +160,9 @@ size_t syscall_arg__scnprintf_hex(char *bf, size_t size, struct syscall_arg *arg
 size_t syscall_arg__scnprintf_ptr(char *bf, size_t size, struct syscall_arg *arg);
 #define SCA_PTR syscall_arg__scnprintf_ptr
 
+size_t syscall_arg__scnprintf_ksym(char *bf, size_t size, struct syscall_arg *arg);
+#define SCA_KSYM syscall_arg__scnprintf_ksym
+
 size_t syscall_arg__scnprintf_int(char *bf, size_t size, struct syscall_arg *arg);
 #define SCA_INT syscall_arg__scnprintf_int
 
-- 
2.55.0

[PATCH perf-tools-next 2/3] perf trace: Auto-assign kernel symbol beautifier to function pointer fields

[Aaron Tomlin]

Tracepoint fields that convey kernel function pointers, such as function,
fn, work, action, and callsite are currently formatted as generic
hexadecimal pointers by default.

Enhance syscall_arg_fmt__init_array() to automatically detect these
fields by name and type signature (e.g., typedefs ending with _func_t
or _fn, or C function pointer types containing (*)) and assign
SCA_KSYM as their default beautifier.

Additionally, register common function pointer field names within the
sorted syscall_arg_fmts__by_name lookup table. This ensures tracepoint
arguments such as workqueue:workqueue_execute_start.function are
symbolised automatically without requiring explicit per-event
configuration. For example:

    ❯ sudo tools/perf/perf trace --event workqueue:workqueue_execute_end --max-events 2 --show-cpu
         0.000 [000] kworker/u32:15/236682 workqueue:workqueue_execute_end(work: 0xffffffffab2f1420, function: toggle_allocation_gate)
         0.132 [000] kworker/u32:15/236682 workqueue:workqueue_execute_end(work: 0xffff8ac2c1adc010, function: flush_to_ldisc)

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 tools/perf/builtin-trace.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 102221b301a5..825b16581581 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -2091,8 +2091,13 @@ static int syscall__alloc_arg_fmts(struct syscall *sc, int nr_args)
 }
 
 static const struct syscall_arg_fmt syscall_arg_fmts__by_name[] = {
+	{ .name = "action",	.scnprintf = SCA_KSYM, },
+	{ .name = "callsite",	.scnprintf = SCA_KSYM, },
+	{ .name = "fn",		.scnprintf = SCA_KSYM, },
+	{ .name = "function",	.scnprintf = SCA_KSYM, },
 	{ .name = "msr",	.scnprintf = SCA_X86_MSR,	  .strtoul = STUL_X86_MSR,	   },
 	{ .name = "vector",	.scnprintf = SCA_X86_IRQ_VECTORS, .strtoul = STUL_X86_IRQ_VECTORS, },
+	{ .name = "work",	.scnprintf = SCA_KSYM, },
 };
 
 static int syscall_arg_fmt__cmp(const void *name, const void *fmtp)
@@ -2193,6 +2198,14 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
 		    ((len >= 4 && strcmp(field->name + len - 4, "name") == 0) ||
 		     strstr(field->name, "path") != NULL)) {
 			arg->scnprintf = SCA_FILENAME;
+		} else if (strcmp(field->name, "fn") == 0 ||
+			   strcmp(field->name, "function") == 0 ||
+			   strcmp(field->name, "callsite") == 0 ||
+			   strcmp(field->name, "action") == 0 ||
+			   (field->type && (strstr(field->type, "(*)") != NULL ||
+					    strstr(field->type, "_func_t") != NULL ||
+					    strstr(field->type, "_fn") != NULL))) {
+			arg->scnprintf = SCA_KSYM;
 		} else if ((field->flags & TEP_FIELD_IS_POINTER) || strstr(field->name, "addr") ||
 			   field_has_hex_fmt(field, len))
 			arg->scnprintf = SCA_PTR;
-- 
2.55.0

[PATCH perf-tools-next 3/3] perf trace: Enhance BTF type formatting to symbolise kernel function pointers

[Aaron Tomlin]

When BTF (BPF Type Format) metadata is loaded from vmlinux, perf trace can
inspect the precise C types of tracepoint and system call parameters.
However, function pointer arguments are currently not recognised during BTF
pretty-printing and default to hexadecimal output.

Introduce btf_is_func_ptr() to inspect BTF type hierarchies
(i.e., traversing pointers, typedefs, and type modifiers) to determine
whether a parameter resolves to a function prototype (BTF_KIND_FUNC_PROTO).

Generalise BTF type caching via syscall_arg_fmt__cache_btf_type() to handle
structs, unions, enums, and function pointers alike. When a field is
identified as a kernel function pointer, trace__btf_scnprintf() routes its
value to syscall_arg__scnprintf_ksym(), enabling automatic zero-config
symbolisation of kernel function pointers whenever BTF is available.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 tools/perf/builtin-trace.c | 39 ++++++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 825b16581581..94dc720a2b3a 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -974,21 +974,43 @@ static size_t syscall_arg__scnprintf_getrandom_flags(char *bf, size_t size,
 #define SCA_GETRANDOM_FLAGS syscall_arg__scnprintf_getrandom_flags
 
 #ifdef HAVE_LIBBPF_SUPPORT
-static void syscall_arg_fmt__cache_btf_enum(struct syscall_arg_fmt *arg_fmt, struct btf *btf, char *type)
+static bool btf_is_func_ptr(const struct btf *btf, const struct btf_type *type)
+{
+	while (type) {
+		if (btf_is_ptr(type)) {
+			type = btf__type_by_id(btf, type->type);
+			return type && btf_is_func_proto(type);
+		}
+		if (btf_is_typedef(type) || btf_is_mod(type)) {
+			type = btf__type_by_id(btf, type->type);
+		} else {
+			break;
+		}
+	}
+	return false;
+}
+
+static void syscall_arg_fmt__cache_btf_type(struct syscall_arg_fmt *arg_fmt,
+					    struct btf *btf, char *type)
 {
 	int id;
 
-	type = strstr(type, "enum ");
 	if (type == NULL)
 		return;
 
-	type += 5; // skip "enum " to get the enumeration name
+	if (strstarts(type, "enum "))
+		type += 5;
+	else if (strstarts(type, "struct "))
+		type += 7;
+	else if (strstarts(type, "union "))
+		type += 6;
 
 	id = btf__find_by_name(btf, type);
 	if (id < 0)
 		return;
 
 	arg_fmt->type = btf__type_by_id(btf, id);
+	arg_fmt->type_id = id;
 }
 
 static bool syscall_arg__strtoul_btf_enum(char *bf, size_t size, struct syscall_arg *arg, u64 *val)
@@ -1023,8 +1045,7 @@ static bool syscall_arg__strtoul_btf_type(char *bf, size_t size, struct syscall_
 		return false;
 
 	if (arg->fmt->type == NULL) {
-		// See if this is an enum
-		syscall_arg_fmt__cache_btf_enum(arg->fmt, btf, type);
+		syscall_arg_fmt__cache_btf_type(arg->fmt, btf, type);
 	}
 
 	// Now let's see if we have a BTF type resolved
@@ -1111,8 +1132,7 @@ static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg *arg,
 		return 0;
 
 	if (arg_fmt->type == NULL) {
-		// Check if this is an enum and if we have the BTF type for it.
-		syscall_arg_fmt__cache_btf_enum(arg_fmt, trace->btf, type);
+		syscall_arg_fmt__cache_btf_type(arg_fmt, trace->btf, type);
 	}
 
 	// Did we manage to find a BTF type for the syscall/tracepoint argument?
@@ -1123,6 +1143,8 @@ static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg *arg,
 		return btf_enum_scnprintf(arg_fmt->type, trace->btf, bf, size, val);
 	else if (btf_is_struct(arg_fmt->type) || btf_is_union(arg_fmt->type))
 		return btf_struct_scnprintf(arg_fmt->type, trace->btf, bf, size, arg);
+	else if (btf_is_func_ptr(trace->btf, arg_fmt->type))
+		return syscall_arg__scnprintf_ksym(bf, size, arg);
 
 	return 0;
 }
@@ -2566,7 +2588,8 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 
 			default_scnprintf = sc->arg_fmt[arg.idx].scnprintf;
 
-			if (trace->force_btf || default_scnprintf == NULL || default_scnprintf == SCA_PTR) {
+			if (trace->force_btf || default_scnprintf == NULL ||
+			    default_scnprintf == SCA_PTR || default_scnprintf == SCA_KSYM) {
 				btf_printed = trace__btf_scnprintf(trace, &arg, bf + printed,
 								   size - printed, val, field->type);
 				if (btf_printed) {
-- 
2.55.0